Method and apparatus for heat treating high speed steel



Jan. 7, 1936. c. B. SADTLER- 2,027,065

METHOD AND APPARATUS FOR HEAT TREATING HIGH SPEED STEEL Filed Oct. 15,1930 ATTORNEY-5 Patented Jan. 7, 1936 PATENT OFFICE r METHOD ANDAPPARATUS FOR HEAT TREATING HIGH SPEED STEEL Chester B. Sadtler,Rockford, 111., assignor to Barher-Colman Company, Rockford, 111., acorporation of Illinois Application October 15, 1930, Serial No. 488,773

9 Claims.

The invention relates generally to the heat treating of steel and moreparticularly to a method and apparatus for heat treating high speed toolsteel.

The general object of the invention is to provide a new and improvedmethod and apparatus for heat treating steel which will function at hightemperatures without causing scaling or other deterioration of thesurface of the steel.

Another object is to provide a novel apparatus together with an improvedmethod whereby tools already formed and sharpened may be heatedrelatively slowly and uniformly to high temperatures without losingtheir form or cutting edge and so that any distortion or enlargement isuniform in character and readily compensated for.

Another object is to provide a new and improved apparatus for heating atreating bath uniformly and to the desired high temperature withoutundue deterioration of the container for the bath or the article beingtreated.

Further objects and advantages will become apparent from the followingdetailed description taken in connection with the accompanying drawing,in which:

Figure 1 is a central vertical section through a preferred form of theapparatus.

Fig. 2 is a plan view thereof with certain portions broken away.

Fig. 3 is a fragmentary section along the line 3-3 of Fig. 1.

While the invention is susceptible of embodiment in many diflerentforms, I have shown in the drawing and shall herein described in detailone such embodiment with the understanding that the present disclosureis to be considered as an exemplification of the principles of theinvention and is not intended to limit the invention to the embodimentillustrated. The scope of the invention will be pointed out in theappended claims.

As illustrated in the drawing the preferred form of the inventioncomprises a furnace having a base portion 5., an annular side wall 6positioned'on and extending upwardly from said base portion andsurrounding a recess 1 in the base portion, and a cover 8 positioned onthe wall and substantially closing the upper end thereof. These parts ofthe furnace define a central furnace chamber 9 the floor of which isformed by a refractory bed Ill positioned in the recess 1.

A crucible or container H is positioned on the floor of the chamber 9and contains a bath l2 in which the articles to be treated are immersedduring the treating process. This container is pref erably made of purenickel. It is herein shown surrounded by an annular wall or muflle I3,of a material having a high thermal conductivity such as bonded siliconcarbide or carborundum, which is spaced uniformly from the containerwall and 5 extends above the top thereof and is arranged to transmitheat to the container and heat the container and bath uniformly ashereinafter more fully described. The bath in the preferred form of theinvention is substantially pure fused boric 10 oxide, the container llbeing open at its upper end so that an article such as a cutter l4, maybe inserted by means of a suspending rod I5.

The floor It as indicated herein comprises a layer of crushed fusedalumina which is placed 15 upon a layer of brick IS. The crushed fusedalumina may be placed in the bottom of the furnace and rammed to ascompact a mass as is possible. A bed comprising approximately fiftypercent crushed fused alumina of one-half to one and one-half inch sizeand fifty percent of four to sixteen mesh has been used with success. Inthis way an eifective support is provided so that when the carborundummullle and nickel container are placed on top of this alumina bed andthe furnace is brought up to temperature, there is no appreciablesettling of either the muflle or nickel container. The alumina isunaffected either chemically or mechanically, by the carborundum ornickel and is substantially non-sintering. If, during operation of theapparatus boric oxide should drip onto the furnace floor, the crushedfused alumina is preferably agitated or worked at intervals ofapproximately a month so as to prevent the alumina from sintering.

The cover 8 of the. furnace comprises side tiles I1, baflle bricks l8 atthe ends and a pair of laterally movable doors l9 and 20. As indicatedmost clearly in Fig. 3 the bricks 3 project over the combustion chamberand form baflles' which force the furnace gases to pass over the upperedge of the carborundum mufile and thence outward under the slidingdoors. I'he doors are herein disclosed as having bricks 2| protectingtheir lower sides and are mounted by means of ball bearings 22 onrectilinear ways 23 so as to permit them to be separated and enable anoperator to insert and withdraw materials into and from the bath. Thedoors are preferably covered by sheet nickel pans 24 which cover theentire doors and serve to collect any boric oxide which may drip fromthe cutters as they are removed from the bath and also drippings whenthe container is bailed out. This effectively prevents rapiddeterioration of the brick work which might otherwise become somewhatimpregnated by the boric oxide.

The nickel container holding the bath of fused boric oxide is heateduniformly by the muffle l3 which surrounds and is uniformly spaced fromthe Wall of the container. The cylindrical wall 6 of the furnace isprovided with openings 25 for tuyeres for the admission of combustiongases. These openings are preferably positioned so that the gases willbe admitted in lines tangent to the cylindrical muflle I3. This producesa rotary movement of the gases around the muffle and help to maintain amore uniform temperature in the furnace. Since the muffle extends abovethe top of the container, cold spots above the bath are avoided. Thetemperature of the bath may be determined by a suitable thermo-electricpyrometer 26, a second pyrometer 21 being preferably provided toindicate the temperature surrounding the container.

By using pure nickel for the container for the boric oxide bath there isno constituent present which will oxidize under the conditions ofordinary gas fired furnaces. The combustion gases admitted to thefurnace produce a flame which has a slightly reducing effect withrespect to the nickel so that there is no oxidation at the temperaturesmaintained. The high melting point of nickel provides ample margin inhigh speed steel treating wherein the temperature rarely exceeds 2400 F.and therefore the container does not contaminate the bath with metallicoxides. Furthermore there is no rapid deterioration of the container.

The process consists in immersing one or more tool blanks, such as theformed cutter I4, suspended on a nickel rod, into the bath of fusedboric oxide in the container. The cutters may be either preheated or maybe immersed cold. If they are cold the initial heating is at arelatively slow and uniform rate since a film of boric oxide immediatelycongeals around each cutter and acts as an insulating material andprevents direct contact of the cutter with the hot liquid bath, thusenabling the temperature of the cutter to be raised at a practicallyuniform rate throughout its mass. As the melting point of the boricoxide is reached around 900 to 1000 F. this film disappears and theheating proceeds more rapidly due to the direct liquid contact with thecutter. Because of the surrounding muffle, transmission of heat to thecontainer is substantially uniform and uniform heating of the bath isobtained.

The pyrometer 25 provides a check on the temperature and hence on theheating and as the temperature approaches the desired point, the cuttermay be inspected to see if it is finished. When the treatment isfinished, as determined preferably by color and light test, it isremoved from the boric oxide bath and quickly subjected to the nextoperation which is generally a cooling medium. When cutters arewithdrawn from the container the viscosity of the molten boric oxide issuch that it forms a film on the cutters and seals the surface of thecutters against the oxygen of the air. Although this film of boric oxidehardens quickly on cooling, it is readily soluble in an alkalinesolution such as sodium carbonate and is useful in protecting cuttersand preventing oxidation while they are being transported from thetreating bath to the cooling medium. The transposition of the cuttersfrom one bath to the other is effected very quickly while oxidation. thebath attack the container appreciably, it has the film of boric oxide iseffective to prevent exposure of the cutters to the air.

After the cutters have been removed from the fused boric oxide bath theymay be given such cooling, drawing and other treatments as may bedesired.

The apparatus as disclosed herein is particularly adapted for successfuland efficient use of the method. The provision of a cylindrical mufiiesurrounding and extending above the bath container provides for uniformheating of the container and bath, and the bed formed of nonsinteringrefractory inaterial provides an effective support for muflle andcontainer. The use of a boric oxide bath in a. nickel container preventsthe formation of metallic oxides and by transferring the heated articlesquickly from the furnace to the cooling means, the film of boric oxideremaining on the articles is effective to prevent Since neither theheating gases nor a long life. Furthermore due to the slow and uniformheating obtained by utilizing the method herein disclosed, anydistortion or enlargement of the cutters is uniform in character and maybe readily compensated for in the preceding forming and sharpeningoperations.

I claim as my invention:

1. An apparatus of the character described comprising, in combination, afurnace having a furnace chamber into which the heating medium isadmitted around the sides, a refractory bed on the floor of saidchamber, a container of pure nickel positioned in the chamber, and a.muffle surrounding and extending above said container and spaceduniformly therefrom for heating said container uniformly.

2. A method for heat treating high speed steel which comprises immersinga steel article into a bath of fused boric oxide, heating said bath tothe desired temperature in a container of pure nickel so as to preventthe formation of metallic oxides in the bath, and transferring theheated article quickly to a quenching medium while the article isprotected from contact with air.

3. A method for heat treating high speed steel which comprises immersinga steel article into a bath of fused boric oxide, heating said bath tothe desired temperature in a container capable of withstanding saidtemperature without causing the formation of metallic oxides in the bathand then quenching the article.

4. A method for heat treating high speed steel which includes immersinga steel article into a bath of fused boric oxide and heating said bathto the desired temperature in a container adapted to prevent theformation of metallic oxides in the bath.

5. A method for heat treating high speed steel which comprises heatingthe steel article to the desired temperature in a bath of fused boricoxide contained in a crucible of pure nickel and then quenching theheated article in an oil bath before any oxidation occurs in air.

6. A method for heat treating high speed steel which comprises heatingthe steel article to the desired temperature in a bath composedsubstantially entirely of fused boric oxide and then quenching theheated article before it becomes oxidized in air.

7. A method for heat treating high speed steel which comprises immersinga steel article into a bath of fused boric oxide preventing theformation of metallic oxides in the bath by holding the bath in acontainer of pure nickel, and maintain- 75 ing uniformity in the heatingofthe bath by a mufile uniformly surrounding and extending above thecontainer.

8. An apparatus of the character described comprising, in combination, afurnace having a furnace chamber into which the heating medium isadmitted around the sides, a refractory bed on the floor of saidchamber, a container of pure nickel positioned in the chamber, a muiflesur- 10 rounding and extending above said container and spaced uniformlytherefrom for heating said container uniformly, and a bath of fusedboric oxide in said container.

9. A method for heat treating high speed steel which includes immersinga steel article into a bath of fused boric oxide and heating said bathto the desired temperature in a nickel container adapted to prevent theformation of metallic oxides in the bath.

CHESTER. B. SADTLER.

